Converging-diverging supersonic shock disruptor for fluid nebulization and drop fragmentation

ABSTRACT

A disrupter apparatus comprises a nozzle comprising: a converging section; a diverging section; and a throat between the converging section and the diverging section. The disrupter apparatus also comprises a holder configured to receive a fluid conduit, which comprises an outlet located in the converging section; and a channel disposed about the holder and configured to guide a gas past the outlet of the fluid conduit, through the converging section, through the throat and into the diverging section where the gas travels at supersonic speed and establishes a standing shock wave in the diverging section. A mass spectrometer and a method are also described.

BACKGROUND

Chemical and biological separations are routinely performed in variousindustrial and academic settings to determine the presence and/orquantity of individual species in complex sample mixtures. There existvarious techniques for performing such separations.

One particularly useful analytical process is chromatography combinedwith mass spectroscopy, which encompasses a number of methods that areused for separating ions or molecules for analysis. Liquidchromatography (‘LC’) is a physical method of separation wherein aliquid ‘mobile phase’ carries a sample containing a mixture of compoundsor ions for analysis (analytes) through a separation medium or‘stationary phase.’ Fluid from the LC device, which comprises both theanalytes and the mobile phase, is provided the analytes to an ion sourceof a mass spectrometer (MS) for spectroscopic analysis.

Often an electro-spray system is used in the interface between the LCdevice and a mass spectrometer. In electro-spray systems, a voltage isapplied to the mobile phase to charge the fluid, and a gas may beprovided to assist in nebulizing the fluid. As the fluid comprising themobile phase and analytes exits a tube or channel annular gas flowaround the tube or channel exit forms drops from the fluid. The fluiddrops have a charge and, as the mobile phase begins to evaporate, thecharge can be transferred to the analytes.

Unfortunately, and among other shortcomings, known drying methods arecomparatively low-energy processes and therefore require the drops totravel a significant distance to desolvate. Moreover, repulsion of ionsdue to known space charge repulsion causes rarefaction. Decreased sampledensity translates to a comparatively small fraction of the sample ionsentering the MS and, hence, reaching a detector in the MS. As such, theefficiency of the MS is reduced.

What is needed, therefore, is a method and apparatus for providinganalytes from an LC column to a mass analyzer that overcomes at leastthe drawbacks of known devices and methods described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present teachings are best understood from the following detaileddescription when read with the accompanying drawing figures. Thefeatures are not necessarily drawn to scale. Wherever practical, likereference numerals refer to like features.

FIG. 1 is a simplified schematic diagram of a mass spectrometer inaccordance with a representative embodiment.

FIG. 2A shows a cross-sectional view of a disruptor apparatus inaccordance with a representative embodiment.

FIG. 2B shows a cross-sectional view of part of a first portion of theapparatus shown in FIG. 2A.

FIG. 3 shows a cross-sectional view of an ionizer in accordance with arepresentative embodiment.

FIG. 4 shows a cross-sectional view of a nozzle provided to a conduit toa mass analyzer in accordance with a representative embodiment.

FIG. 5 shows a flow-chart of a method in accordance with arepresentative embodiment.

DEFINED TERMINOLOGY

It is to be understood that the terminology used herein is for purposesof describing particular embodiments only, and is not intended to belimiting.

As used in the specification and appended claims, the terms ‘a’, ‘an’and ‘the’ include both singular and plural referents, unless the contextclearly dictates otherwise. Thus, for example, ‘a device’ includes onedevice and plural devices.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation andnot limitation, representative embodiments disclosing specific detailsare set forth in order to provide a thorough understanding of thepresent teachings. Descriptions of known systems, devices, materials,methods of operation and methods of manufacture may be omitted so as toavoid obscuring the description of the example embodiments. Nonetheless,systems, devices, materials and methods that are within the purview ofone of ordinary skill in the art may be used in accordance with therepresentative embodiments.

FIG. 1 shows a simplified schematic diagram of a mass spectrometer 100in accordance with a representative embodiment. The block diagram isdrawn in a more general format because the present teachings may beapplied to a variety of different types of mass spectrometers. As shouldbe appreciated as the present description continues, devices and methodsof representative embodiments may be used in connection with the massspectrometer 100. As such, the mass spectrometer 100 is useful ingarnering a more comprehensive understanding of the functions andapplications of the devices and method of the representativeembodiments, but is not intended to be limiting of these functions andapplications. The mass spectrometer 100 includes an ion source 101, amass analyzer 102 and a detector 103. The mass spectrometer 100comprises additional apparatuses, such as electrostatic and RF lenses,as well as other apparatuses not shown. Such apparatuses are known andare not described in detail to avoid obscuring the description ofrepresentative embodiments.

The ion source 101 comprises a disrupter apparatus 104. The disruptorapparatus 104 is configured to receive fluid from an LC device 105 andinert gas from a gas source 106 and functions as an interface betweenthe LC device 105 and the mass spectrometer 100. As described in moredetail below, the disruptor apparatus 104 nebulizes the fluid from theLC device 105 to generate drops and then fragments the drops to formdroplets (not shown in FIG. 1). The droplets are desolvated leavinganalyte ions and gas molecules. The resulting analyte ions (not shown inFIG. 1) are provided to mass analyzer 102. The mass analyzer 102 mayinclude a conduit such as a sleeve, transport device, dispenser,capillary, nozzle, hose, pipe, pipette, port, connector, tube, orifice,orifice in a wall, coupling, container, housing, structure or otherapparatus used to transport analyte ions from the ion source 101 to thedetector 103. The mass analyzer 102 may be one of a number of knowndevices used to filter ions based on a charge-to-mass ratio.Illustratively, the mass analyzer comprises one of a quadrupole massanalyzer, an ion trap, a time-of-flight device, among others. Thedetector 103 may be a known ion detector used to detect the analyte ionsthat are collected and separated by the mass analyzer 102 according totheir mass-to-charge ratio. The detector 103 typically also includesknown hardware, software or firmware, or a combination thereof useful indetecting analytes.

FIG. 2A shows a cross-sectional view of disrupter apparatus 104 inaccordance with a representative embodiment. The disrupter apparatus 104comprises a first portion 201, a second portion 202 and a third portion203. The first portion 201 defines a nozzle 204 that extends axiallythrough the first portion. The nozzle 204 comprises a converging section205, a throat 206 and a diverging section 207 in order, in tandem. Thesecond portion 202 comprises a holder 208, and the first portion 201 isconfigured to receive a part of the holder 208 remote from the throat206 and diverging section 207. The holder 208 maintains an outlet 211 ofa fluid conduit 209 in a position to facilitate nebulization. The fluidconduit 209 is connected at one end to an output of an LC column 210 andprovides fluid at the outlet 211 for nebulization as described morefully below.

In the embodiment shown in FIG. 2A, the holder 208 maintains the fluidconduit 209 in a position such that the outlet 211 is located in thefirst portion 201 at a position in the converging section 205 of thenozzle 204 to facilitate nebulization. In an alternative embodiment, thefluid conduit 209 could be extended through the throat 206 so that theoutlet 211 is located in the diverging section 207 of the nozzle 204.

The third portion 203 is coupled to the second portion 202. In theexample shown, a part of the third portion 203 accommodates a part ofthe second portion 202. The third portion 203 receives a gas 212 from agas control and supply 213. Typically, the gas 212 is an inert gas suchas nitrogen. The LC column 210 is connected to the fluid conduit 209 viaa connection in the third portion 203, and as described provides LCfluid (not shown in FIG. 2A) to the fluid conduit 209 therethrough.

The second portion 202 comprises an axial gas conduit 214 disposed aboutthe fluid conduit 209, and comprises orifices 215 that extend radiallyfrom the axial gas conduit 214 to a channel 216, which is illustrativelyformed by and between the first portion 201 and the second portion 202.The axial gas conduit 214 is configured to direct the gas 212 toward theorifices 215. The orifices 215 are configured to direct the gas 212 intothe channel 216 of the first portion 201 where the gas 212 propels drops(not shown in FIG. 2A) of fluid resulting from nebulization of the fluidprovided at the outlet 211. As described more fully herein, the dropsare propelled by the gas 212 through the converging section 205 and thethroat 206, and into the diverging section 207. The drops are thenpropelled by the gas 212 into a standing shock wave 218 established bythe flow of gas 212 through nozzle 204.

The fluid provided at the outlet 211 of the fluid conduit 209 isnebulized by known methods. Notably, in representative embodiment, thefluid provided at the outlet 211 is nebulized by known electrospraymethods; or by gas-assisted nebulization, by or electrospray withgas-assisted nebulization. The gas 212 may be used to effectgas-assisted nebulization, or in electrospray with gas-assistednebulization. If electrospray is used as the sole method ofnebulization, the gas 212 would not be used in the nebulization of thefluid to form drops, but only to propel the drops through the nozzle 204and into the standing shock wave 218.

In a representative embodiment, the orifices 215 are arranged at 90°intervals about a longitudinal axis 217 through the disruptor apparatus104. In another representative embodiment, the orifices 215 are arrangedat 120° intervals about the longitudinal axis 217. In still otherrepresentative embodiments there are more than four orifices, while inother embodiments there are three or fewer orifices. The regular spacingof the intervals is merely illustrative, and irregular spacing of theorifices 215 is contemplated.

In representative embodiments, the material used for the first portion201 and the fluid conduit 209 is electrically conducting, while thematerial used in the second portion 202 is electrically insulating. Thethird portion 203 may be either electrically conducting or insulating.Illustratively, the electrically conducting material comprises one ormore of a metal, a metal alloy, an electrically conducting compositematerial, or a coated plastic material. Similarly, the insulatingmaterial is illustratively a polymer (e.g., plastic), a compositematerial or other suitable electrical insulator. As will become cleareras the present description continues, the conducting and insulatingmaterials are selected to facilitate establishing an electricalpotential difference between the first portion 201 and the conduit 209.

In accordance with a representative embodiment, in operation, thedisrupter apparatus 104 first nebulizes fluid from the LC column 210 byelectrospray with gas-assisted nebulization of fluid provided at theoutlet 211 disposed in the converging section 205, and by passing thegas 212 past the outlet 211. Alternatively, the nebulization occurssolely by gas assisted nebulization of fluid at the outlet 211 bypassing the gas 212 past the outlet 211. Next, the drops (not shown inFIG. 2A) formed by the nebulization are propelled by the gas 212 throughthe throat 206 and into the diverging section 207. As described morefully herein, the drops attain a substantially greater velocity than thevelocity attained by known nebulization methods, and impact on astanding shock wave 218 located in the diverging section or at or nearan exit 219 of the diverging section 207. The impact of the drops withthe standing shock wave 218 fragments the drops into droplets (not shownin FIG. 2A) by imparting at least three (3) orders of magnitude and asmuch as approximately four (4) orders of magnitude more energy into thedrops than known practice gas assisted nebulization.

The gas 212 is provided at an upstream pressure P₀ that is chosen toestablish the standing shock wave 218. As described more fully herein,the Mach number of the standing shock wave 218, which refers to thestanding shock wave caused by gas 212 having a velocity of the same Machnumber upon entering the standing shock wave 218, is dependent upon theratio of the upstream pressure (P₀) to the ambient pressure ratio (P₃)at the outlet of the diverging section 205. In representativeembodiments, the ratio P₀/P₃ is selected to be on the order ofapproximately 4.0 or higher to attain a desired Mach number to ensuresuitable fragmentation of drops of nebulized fluid. It is noted that theupstream pressure P₀ is more readily controlled than the ambientpressure P₃, which is, for example, the pressure of a chamber of the ionsource 101 and is normally atmospheric pressure.

In accordance with representative embodiments, the disrupter apparatus104 significantly desolvates or substantially completely desolvates themobile phase of the LC fluid leaving analyte ions. Among other benefits,the disrupter apparatus 104 produces a comparatively high density cloudof analyte ions—near the entrance of the mass analyzer 102. By contrast,and as alluded to above, because of the time and distance required todesolvate the fluid drops formed by known low energy drop formation,current nebulizers produce a low-density cloud of analyte ions. As such,using known nebulizers, the nebulizer outlet must be placedcomparatively far from the inlet to the mass analyzer. The extra timeand distance resulting from this separation allow space charge forces tocause the analyte ions to move apart and become less dense. Therefore,by known methods and apparatuses fewer analyte ions are provided to theMS analyzer 102.

In certain embodiments such as described below in connection withconnection FIG. 3, the disrupter apparatus 104 is a component of the ionsource 101. In other embodiments such as described below in connectionwith FIG. 4, the disruptor apparatus 104 functions as the ion source 101and is coupled directly to a conduit to a mass analyzer 102. Thus,whether the disrupter apparatus 104 is a component of the ion source 101or functions as the ion source 101 of the mass spectrometer 100, thedisrupter apparatus 104 comprises an interface between the LC column andthe mass spectrometer.

FIG. 2B is a cross-sectional view showing a part of the first portion201 of the disruptor apparatus 104, which is shown in an enlarged viewto facilitate the description of the nozzle 204. As shown, the throat206 is situated between the converging section 205 and the divergingsection 207; and the throat 206 is a part of nozzle 204 in which thecross-sectional area of the nozzle 204 in the x-z plane orthogonal tothe longitudinal axis 217 is a minimum. Notably, the dashed linesdelineating the boundaries of the converging section 205, the throat 206and the diverging section 207 are set in approximate position.Generally, the converging section 205, as its name implies, is a sectionwhere the cross-sectional area of the nozzle 204 in the x-z planeorthogonal to the longitudinal axis 217 decreases with respect to theaxial position (+x-direction) towards the throat. The diverging section207 is a section where the cross-sectional area of the nozzle in the x-zplane orthogonal to the longitudinal axis 217 increases with axialposition (+x direction) away from the throat 206. Moreover, while thethroat 206 comprises a region of the nozzle 204, it is a point at whichthe cross-sectional area of the nozzle 204 is a minimum.

As noted above, the holder 208 maintains the outlet 211 of the fluidconduit 209 at a location in the first portion 201 at a position in theconverging section 205 of the nozzle 204 to facilitate nebulization.Fluid 222 from the LC column 210 flows through the fluid conduit 209 andthe gas 212 converges about the outlet 211 as it traverses theconverging section 205. The gas 212 converging near the outlet 211assists in nebulizing the fluid 222 at the outlet 211 via shear forcesto generate drops 220.

The gas 212 propels the drops 220 through the converging section 205,through the throat 206 and into the diverging section 207. The ratio ofthe upstream pressure to ambient pressure (P₀/P₃), dimensions of theconverging section 205, the throat 206, and diverging section 207 of thenozzle 204 of disrupter apparatus 104 are selected so that the gas 212flowing through the nozzle 204 creates a standing shock wave 218 at aselected location within the nozzle 204. In certain embodiments, thestanding shock wave is positioned at the exit 219 of the divergingsection 207. In other embodiments, the standing shock wave 218 ispositioned within the diverging section 218, but comparatively close tothe exit 219 of the diverging section 207. As described more fullybelow, the positioning of the standing shock wave 218 away from thethroat 206 affords sufficient distance for the drops 220 to beaccelerated by the gas 212 and thereby attain a comparatively highvelocity before the drops 220 impact the standing shock wave 218. Bysimilar analysis, standing shock wave 218 should not be located inproximity to the throat 206 because the drops 220 will not havesufficient distance to attain a sufficient velocity for acceptablefragmentation of the drops 220 to occur. As such, the pressure ratio(P₀/P₃) and dimensions of the components of the nozzle 204 are selectedto avoid locating the standing shock wave 218 in proximity to the throat206.

The gas 212 attains a velocity of at least approximately Mach 1.2 in thediverging section 207. In certain embodiments, the gas 212 attains avelocity of at least approximately Mach 3.0 in the diverging section207; and in certain embodiments, the gas 212 attains a velocity of atleast approximately Mach 4.0. The comparatively high velocity of the gas212 serves to propel the drops 220 through the diverging section 207 atcomparatively high velocity as well. As they traverse the divergingsection 207, the drops 220 can attain a velocity nearing that of the gas212. The velocity of the drops 220 relative to the gas 212 depends onthe distance between the throat 206 and the standing shock wave 218. Inrepresentative embodiments, by providing a divergent section 207 ofsuitable length, drop velocities of 80% relative to the gas velocity arereadily attainable. The drops 220 attain their maximum velocity in thediverging section 207 and impact the standing shock wave 218 atsubstantially normal incidence. The combination of the comparativelyhigh speed attained by the drops 220 and their substantially normalincidence to the standing shock wave 218 fosters efficient fragmentationof the drops 220.

The normal incidence of the drops 220 to the shock wave 218 is moredisruptive than a network of weak oblique shocks as provided in certainknown nebulizers. As the drops 220 enter the standing shock wave 218,the standing shock wave 218 will flatten the drops 220; deposit acomparatively large vortex ring around the periphery of the drops 220;and create a comparatively large instantaneous difference between thedrop speed and the ambient gas speed, generating shear, which will causethe drops 220 to fission. Drops 220 fragment into droplets 221, andafter emerging from the standing shock wave 218, the droplets 221 entera region at an ambient pressure P₃, and the velocity of the droplets 221reduces very rapidly to ambient gas velocities. This rapid change invelocity imparts energy to the droplets 221 in the form of heat.Accordingly, in a representative embodiment, as the fluid 222 from theLC column 210 travels through the disrupter apparatus 104, it undergoesa gas-assisted nebulization upon mixing with the gas 212 in theconverging section 205; and a high-energy fragmentation caused byaccelerating the drops 220 along a direction normal to and through thehighly energetic shock wave 218. By way of comparison, the energyimparted to the drops 220 by the disruptor apparatus 104 is on the orderof 10³ to 10⁴ greater than the energy imparted by known nebulizerapparatuses and methods for similar upstream and ambient pressures, andinert gas flow rates of inert gas. Illustratively, the energy impartedto the drops 220 with the velocity of gas 212 in the diverging section207 of approximately Mach 3.0 or greater is sufficient to substantiallycompletely desolvate the droplets 221.

As noted previously, the fluid conduit 209 and the first portion 201 areelectrically conductive and the holder 208 is electrically insulating.The insulator allows an optional voltage (designated V in FIG. 2B) to bemaintained between the fluid conduit 209 and the first portion 201 thatthere exists an electrical potential gradient that charges the drop 220as they exit the fluid conduit 209. In a representative embodiment, thefluid conduit 209 is maintained at a ground potential and a positivevoltage is applied to the first portion. The present teachingscontemplate foregoing the establishing of a voltage as just described.Rather, aiding in the imparting of electric charge to drop 220 by theapplication of an electric field at the outlet 211 may be unnecessary asdrops 221 resulting from the fissioning may comprise charged analyteions after passing through the shock wave 218.

Thus, in accordance with a representative embodiment, the disrupterapparatus 104 provides smaller droplets as droplets 221. The droplets221 require a comparatively shorter desolvation time in a drying stageof the ion source. A reduced desolvation time beneficially results in ahigher density analyte ion cloud near the inlet to the mass analyzer102. Ultimately, this higher analyte ion density produces a greater ioncurrent into the mass analyzer 102, which in turn leads to highersensitivity and lower detection levels.

Referring to FIGS. 2A and 2B, and as alluded to above, in theconverging/diverging nozzle of disrupter apparatus 104, the ratio ofpressures, P₀/P₃ and the dimensions of the exit 219 of diverging section207 and the throat 206 of the nozzle 204 dictate the conditions for bothsupersonic flow of gas 212 and the location of the standing shock wave218. In accordance with representative embodiments, the gas 212traveling through the nozzle 204 of the disrupter apparatus 104 canreadily attain a velocity in the diverging section 207 of at least M=1.2and more typically in the range of approximately M=3 to approximatelyM=4. By way of quantitative example, a minimum pressure ratio of P₀/P₃that must be exceeded to achieve supersonic speeds is 1.89 where the gas212 is air or, likewise, nitrogen. As such, with the a pressure ratioP₀/P₃ of approximately 2 or greater, the gas 212 can attain supersonicspeeds in the diverging section 207, the standing shock wave 218 can beestablished, and the fragmentation of drops 220 into droplets 221 can beachieved.

As noted above, the cross-sectional area of the exit 219 of thediverging section 207 and the cross-sectional area of the throat 206impact the position of the standing shock wave 218. A given specifiedupstream pressure P₀ and downstream post-shock pressure P₃ determine theratio of the area of the exit 219 of the diverging section 207 to thearea of the throat 206 that ensures that the standing shock wave 218exists and is situated at the exit 219 of the diverging section 207. Bycreating the nozzle 204 with this area ratio, or substantially with thisarea ratio, a standing shock wave 218 substantially normal to thelongitudinal axis 217 is formed at the exit 219. For example, selectingambient pressure P₀ to be approximately 4 atm, which can be readilyachieved, a design Mach number is required so that the pre-shock wavestatic pressure P₁ begets the post-shock pressure P₂ that issubstantially equal to the ambient pressure P₃, which is illustratively1 atm.

Many details of attaining supersonic gas flow in a convergent/divergentnozzle and the positioning of a standing shock wave are known. Suchdetails, can found, for example, in Section 7.2 of C. J. Chapman, “HighSpeed Flow”, Cambridge University Press (2000), ISBN 0-521-66647-3. Thedisclosure of this section of this text is specifically incorporatedherein by reference.

In known methods of nebulization used in many LC applications, thepredominant mechanism causing drop fissioning is not kinetic energy (KE)deposition resulting from the interaction of the drops with a standingshock wave according to the representative embodiments described above,but rather electrostatic repulsion/fissioning of drops as the mobilephase evaporates. In known apparatuses and systems, space charge, whichis a term used to describe mutual electrostatic repulsion of analyteparticles and drops, limits maximum transmission not to a fraction ofthe total number of analyte particles, but to a maximum absolutequantity. That is, the space charge limit is reached for ions in aparticular device, attempts to increase analyte throughput does nothelp. In contrast, during the comparatively rapid fragmentation of drops220 into droplets 221, the droplets 221 acquire a static electric chargedue to non-uniform distribution of charge in the original drop as wellas the splitting of polarized molecules. Moreover, one way to mitigatespace charge quenching of analyte current is to decrease the residencytime ions spend in desolvation. Therefore, by desolvating the droplets221 more rapidly and providing the ions into the mass analyzer morequickly, the maximum current (in absolute value) is increased. Inembodiments described herein, because the droplets 221 are comparativelysmall, a comparatively greater area-to-volume ratio is attained and thespeed of desolvation is increased compared to known methods andapparatuses. As described below, the nozzle of disrupter apparatus 104beneficially improves the speed of desolvation, increasing thespace-charge-limited current and allowing more analytes to be passedinto the mass spectrometer device. These and other beneficial aspects ofthe apparatus are described presently in connection with representativeembodiments shown in FIGS. 3 and 4.

FIG. 3 is a cross-sectional view of ion source 101 in accordance with arepresentative embodiment. The ion source 101 comprises a housing 300and the disruptor apparatus 104, which extends through the housing 300into a chamber 301 bounded by the housing 300. Droplets 221 emerge fromthe diverging section 207 of the nozzle 204 of disrupter apparatus 104and enter the chamber 301. In a representative embodiment, the divergingsection 207 is oriented along a longitudinal axis 302 that issubstantially orthogonal to a conduit longitudinal axis 303 of a conduit304. While the orthogonal arrangement may be used, it is not essential.A variety of angles (obtuse and acute) may be defined between thelongitudinal axis 302 and the longitudinal axis 303 of the conduit 304.Alternatively, the longitudinal axis 302 may be aligned with thelongitudinal axis 303 of the conduit 304. Illustratively, the pressurein the chamber 301 is maintained at about 20 Torr to about 2000 Torr.Operation at atmospheric pressure (around 760 Torr) and non-atmosphericpressure is thus possible.

The mass analyzer 102 includes the conduit 304 or any number ofcapillaries, conduits or devices for receiving and moving the analyteions from the chamber 301 to the detector 103. The conduit 304 extendsinto the housing 300 downstream from the disrupter apparatus 104. Theconduit 304 may comprise a skimmer (not shown in FIG. 3) that guides theanalyte ions to the conduit 304, which in turn guides the analyte ionsto the detector into the mass analyzer 102 and ultimately to thedetector 103 (not shown in FIG. 3). Optionally, a gas conduit 309 maydirect a drying gas 305 into the chamber 301 toward the droplets 221 inthe chamber 301. The drying gas 305 is heated and assists further indesolvating droplets 221.

In a representative embodiment, the droplets 221 that emerge from thedisrupter apparatus 104 are electrically charged. A voltage isestablished between the disrupter apparatus 104 and the conduit 304 sothat the charged analyte ions are directed to the conduit 304 alongtrajectories 306. Most of the droplets 221 that are not provided to theconduit 304 continue to travel in the direction of the longitudinal axis302 and are expelled at an exhaust port 308 along with gases 307.

As described above, providing droplets 221 of a smaller volume fostersmore efficient separation of the mobile phase from the analytes. This isbecause the amount of time it takes for a droplet 221 to desolvate themobile phase is directly related to the size of the drop: drops oflesser volume desolvate more rapidly than drops of greater volume.Faster desolvation time in turn means not only that a larger fraction ofanalyte ions are desolvated, but also means the distance that droplets221 travel from outlet 211 until they are desolvated is shorter. In manyknown methods and apparatuses, many analyte ions are not ultimatelyprovided to the mass analyzer 102, but rather are lost such as throughan exhaust 307. Often in known devices, the drops are lost beforeseparation of the mobile phase and analytes occurs. By contrast, thedroplets 221 are desolvated more rapidly and in a shorter distance, orin a smaller volume in the ion source 101 of FIG. 3. This facilitatesmore efficient transfer of analyte ions into the mass analyzer 102 byreducing space charge effects, which are the mutual electrostaticrepulsion of ions as well as charged droplets 221.

Because disruptor apparatus 104 fragments the drops 220 (FIG. 2B) intodroplets 221 of a comparatively small volume and the desolvation processoccurs more rapidly. In certain embodiments, the droplets 221 may beprovided directly to the conduit 304 and thus directly to the massanalyzer 102. In this manner, the disruptor apparatus 104 functions asan interface between the LC column and the mass spectrometer.Representative embodiments illustrating the use of the apparatus as suchan interface are described presently in conjunction with FIGS. 4.

FIG. 4 shows cross-sectional views of the disrupter apparatus 104provided to a conduit to a mass analyzer in accordance withrepresentative embodiments. Many of the details provided in connectionwith the description of representative embodiments of FIGS. 1, 2A, 2Band 3 are germane to the presently described embodiments, and are notrepeated in order to avoid obscuring the description of the embodimentof FIG. 4.

Specifically, FIG. 4 shows a cross-sectional view of a part of the firstportion 201 of the disrupter apparatus 104 and a conduit 403 to a massanalyzer (not shown in FIG. 4) in accordance with a representativeembodiment. Notably, the housing 300, the chamber 301, and similarcomponents described in connection with representative embodiments inconnection with FIG. 3 are not included in the presently describedembodiment. Rather, the droplets 221 provided from the diverging section207 of the nozzle 204, travel generally along a trajectory 401, and areprovided directly to the conduit 304 to the mass analyzer. In thismanner, the disrupter apparatus 104 functions as the ion source 101. Asdescribed in detail above, because the drops 220 have been fragmentedinto droplets 221 of comparatively small volumes, the time required fordesolvation is reduced; and the distance that droplets 221 need totravel until the droplets 221 are desolvated is shorter. As such, thenozzle 204 of disruptor apparatus 104 may be provided directly to theconduit 304 to the mass analyzer 102.

In the present embodiment, the nozzle 204 and the conduit 403 share acommon axis of symmetry 402, which is co-axial with the trajectory 401of the droplets 221 passing from the nozzle 204 to the conduit 403. Thenozzle 204 and the conduit 403 may be integral. Illustratively, thedrops 220 from the outlet 211 traverse the throat 206 and are fragmentedinto droplets 221 by the standing shockwave 218 as described above. Thedroplets 221 are substantially completely desolvated, travel down theconduit 403 and are provided to the mass analyzer. Because of thecomparatively short distance required for desolvation to occur, agreater portion of the analyte ions from the desolvated droplets 221 areprovided to the conduit 403, and then to the mass analyzer through thecomparatively direct connection of the nozzle to the conduit 403.

FIG. 5 shows a flow-chart of a method 500 in accordance with arepresentative embodiment. Many of the details provided in connectionwith the description of representative embodiments of FIGS. 1, 2A, 2B, 3and 4 are germane to the presently-described embodiment, and are notrepeated in order to avoid obscuring the description of the illustrativemethod.

At 501, the method comprises introducing a gas into the convergingsection of the nozzle at an upstream pressure. At 502, the methodcomprises subjecting the diverging section of the nozzle to an ambientpressure so that a ratio of the upstream pressure to the ambientpressure creates a standing shock wave in the diverging section. At 503,the method comprises mixing a fluid comprising an analyte with the gasto form drops directed towards the standing shock wave. The mixing isdone in the converging section.

In view of this disclosure it is noted that the methods and devices canbe implemented in keeping with the present teachings. Further, thevarious components, materials, structures and parameters are included byway of illustration and example only and not in any limiting sense. Inview of this disclosure, the present teachings can be implemented inother applications and components, materials, structures and equipmentto needed implement these applications can be determined, whileremaining within the scope of the appended claims.

1. In a disruptor apparatus comprising a nozzle, the nozzle comprising athroat, a converging section and a diverging section in tandem, a methodcomprising: introducing a gas into the converging section of the nozzleat an upstream pressure; subjecting the diverging section of the nozzleto an ambient pressure so that a ratio of the upstream pressure to theambient pressure creates a standing shock wave in the diverging section;and in the converging section, mixing a fluid comprising an analyte withthe gas to form drops directed towards the standing shock wave.
 2. Amethod as claimed in claim 1, wherein the mixing the fluid with the gasnebulizes the fluid to form the drops, the drops having a first size. 3.A method as claimed in claim 2, wherein the standing shock wavefragments the drops having the first size into droplets having a secondsize that is smaller than the first size.
 4. A method as claimed inclaim 3, wherein the mixing comprises a first nebulizing and thefragmenting comprises a second nebulizing.
 5. A method as claimed inclaim 1, wherein the diverging section comprises an exit and thestanding shock wave and the standing shock wave is located adjacent tothe exit.
 6. A method as claimed in claim 1, further comprisingsubjecting the converging section of the nozzle to an electric field. 7.A method as claimed in claim 1, wherein the inert gas attains a velocityin the diverging section at a speed of approximately Mach 2.0 orgreater.
 8. A method as claimed in claim 3, wherein the fragmentingsubstantially desolvates the droplets into ions and gas molecules.
 9. Adisrupter apparatus, comprising: a nozzle comprising: a convergingsection; a diverging section; and a throat between the convergingsection and the diverging section; a holder configured to receive afluid conduit, which comprises an outlet located in the convergingsection; and a channel disposed about the holder and configured to guidea gas past the outlet of the fluid conduit, through the convergingsection, through the throat and into the diverging section where the gastravels at supersonic speed and establishes a standing shock wave in thediverging section.
 10. A disruptor apparatus as claimed in claim 9,wherein the gas at least assists in nebulizing a fluid emerging from theoutlet of the fluid conduit to form drops of a first size.
 11. Adisrupter apparatus as claimed in claim 10, wherein the standing shockwave is formed at or near an exit of the diverging section.
 12. Adisrupter apparatus as claimed in claim 11, wherein the drops areincident on the standing shock wave, and are fragmented by the shockwave into droplets of a second size that is smaller than the first size.13. A disruptor apparatus as claimed in claim 9, wherein the nozzle andthe fluid conduit are defined in an electrically-conducting material,and the holder is electrically insulating.
 14. A mass spectrometer,comprising: a disrupter apparatus, comprising: a nozzle comprising: aconverging section; a diverging section; and a throat between theconverging section and the diverging section; a holder configured toreceive a fluid conduit, which comprises an outlet located in theconverging section; and a channel disposed about the holder andconfigured to guide a gas past the outlet of the fluid conduit, throughthe converging section, through the throat and into the divergingsection where the gas travels at supersonic speed and establishes astanding shock wave in the diverging section a nozzle comprising: aconverging section; a
 15. A mass spectrometer as claimed in claim 15,wherein the gas at least assists in nebulizing a fluid emerging from theoutlet of the fluid conduit to form drops of a first size.
 16. A massspectrometer as claimed in claim 16, wherein the standing shock wave isformed at or near an exit of the diverging section.
 17. A massspectrometer as claimed in claim 18, wherein the drops are incident onthe standing shock wave, and are fragmented by the shock wave intodroplets of a second size that is smaller than the first size.
 18. Amass spectrometer as claimed in claim 15, wherein the nozzle and thefluid conduit are defined in electrically-conducting material, and theholder is electrically insulating.